Update: although the post was initially written for Galaxy Note with ICS, the method actually works for Galaxy Note 2, Galaxy Note 3 and many other Android devices with different versions of Android.

After ICS update, some Galaxy Note users complained about poorer battery life compared with that with Gingerbread. Initially, I thought it is a problem of “feeling” because I personally felt similar battery life after the ICS update. I was a bit disappointed because I had expected some sort of battery life improvements.

Suddenly, last week, I encountered the battery drain issue: battery just draining crazily. In one hour it can drain 3-10% battery capacity when the phone is idle. So, I know the users complaining are not alone.

As I finished my investigation and found the culprit, now I share with you how to solve battery issues on your Galaxy Note after the ICS Update. If you already have battery issues or you feel you have battery issues, you may follow my steps.

First, I installed an free app called CPU Spy (https://play.google.com/store/apps/details?id=com.bvalosek.cpuspy), which will give you the duration of each CPU state. When your phone is idle (screen off, no music playing, no downloading), normally, your CPU should be in “Deep Sleep” state. For example, after one night, you check your CPU Spy, it should look like this.

As you can see, this is the normal situation. In the night, 95%of the time, the CPU is in deep sleep, and after 11 hours, about 6% battery was drained (I also checked emails before sleep). If your phone does not go to deep sleep, you will find the duration on other state is higher. Very likely, you have battery drain issues if more than 20% battery are drained when you are sleeping (6-10 hours), You probably will find far larger percentage on 200MHz state. If more than 30% are drained in one night, very likely, your phone never goes to Deep Sleep state.